Ultrasound intensification of two‐stage biodiesel production: optimization for palm empty fruit bunch oil as a palm oil industry by‐product

Abstract

Palm empty fruit bunch oil (palm EFB oil) is a waste product that can be used to produce biodiesel at a low cost. However, high free fatty acid (FFA) content is the primary obstacle to biodiesel production. Before the transesterification process can begin, the oil must be esterified to reduce its acid content. This study seeks to employ dual‐frequency ultrasound at frequencies of 28 kHz (200 W) and 40 kHz (200 W) to aid in the esterification and transesterification of ZSM‐5‐38 and CaO catalysts, respectively. Central composite design and response surface methodology were used to determine the optimal conditions for the three primary parameters of methanol to oil (M:O molar ratio), catalyst loading and reaction time. A 12:1 M:O molar ratio, 11.36 wt% catalyst loading (ZSM‐5‐38) and 60 min of reaction duration were the optimal conditions for esterification to achieve a FFA conversion of 91.51%. The reusability of ZSM‐5‐38 revealed a decrease in FFA conversions of 87.36, 75.11, 67.13 and 58.68% with each reused cycle. The optimal transesterification conditions were a 3.28:1 M:O molar ratio, 4.62 wt% catalyst loading (CaO) and 64 min of reaction time, yielding 83.58% biodiesel. The viscosity value (D 445), the flash point (D 93) and the heating value (ASTM D240) of biodiesel produced under optimal conditions were evaluated. The biodiesel properties were determined to be 4.7931 mm2/s, 176°C and 40 398 kJ/kg, respectively.